A workpiece, such as a semiconductor wafer, is subject repeatedly to single-wafer processing processes, such as a film deposition process, an etching process, a thermal process, a modifying process and a crystallization process to build a desired semiconductor integrated circuit on the workpiece. Those processes use necessary process gases. For example, the film deposition process uses film forming gases, the modifying process uses ozone gas, the crystallization process uses an inert gas, such as N2 gas, and O2 gas. Those process gases are supplied into a processing vessel.
For example, a single-wafer thermal processing system for processing a single wafer at a time by a heat treatment process places a support table internally provided with, for example, a resistance heater in a processing vessel capable of being evacuated, supplies predetermined process gases into the processing vessel after mounting a semiconductor wafer on top of the support table, and processes the wafer by various thermal processes under predetermined process conditions.
The support table is disposed in the processing vessel with its surface exposed to the atmosphere in the processing vessel. Therefore, a small amount of heavy metals contained in materials of which the support table is made, for example, a ceramic material, such as AlN, and metallic materials is caused to diffuse into the interior space of the processing vessel by heat. Those diffused substances cause metal contamination and organic contamination. Very severe contamination preventing measures have been desired to prevent metal contamination and organic contamination in recent years where organometallic compounds are used as source gases for film deposition.
Usually, the heater incorporated into the support table is divided into a plurality of concentric circular sections. The respective temperatures of the sections are controlled individually to heat the support table in an optimum temperature distribution for processing a wafer. If magnitudes of power supplied to the sections of the heater are greatly different from each other, parts of the support table respectively corresponding to the sections of the heater are subject to greatly different thermal expansions, respectively, and, in some cases, the support table breaks. The insulation resistance of AlN decreases greatly and leakage current flows when AlN is exposed to high-temperature heat. Therefore, process temperature has been unable to be increased beyond about 650° C.
When the thermal process is a film deposition process for depositing a thin film on a surface of a wafer, unnecessary films are deposited inevitably on the surface of the support table and the inside surfaces of the processing vessel in addition to the deposition of a desired film on a surface of the wafer. If the unnecessary films come of the surfaces of the support table and the processing vessel, particles that reduce product yield are produced. A cleaning process is executed periodically or at indeterminate intervals to remove the unnecessary films. The cleaning process etches off the unnecessary films by supplying an etching gas into the processing vessel or removes the unnecessary films by immersing structural members disposed inside the processing vessel in an etchant, such as a nitric acid solution.
A technique for contamination prevention or reducing the frequency of the cleaning process proposed in JP 63-278322 A forms a support table by covering a heating element with a quartz casing. A technique for the same purpose proposed in JP 07-078766 A uses a support table constructed by placing a resistance heating element in a quartz case. Techniques proposed for the same purpose in JP 03-220718 A and JP 06-260430 A use a support table formed by sandwiching a heater between quarts plates.
Those prior art techniques using a support table covered with a quartz cover are effective in suppressing contamination, such as metal contamination, to some extent. However the effect of the prior art techniques is not fully satisfactory. When the quarts plates are transparent, a temperature distribution on the heating element is reflected on the temperature of the wafer and the wafer is hated in an uneven intrasurface temperature distribution. Moreover, in some cases, unnecessary films are deposited in patches or irregularities on the back surface of the support table or on a cover covering the back surface of the support table. Since thick parts and thin parts of the unnecessary films deposited in patches or irregularities have different emissivities, respectively. Consequently, temperature is distributed in an uneven temperature distribution on the surface of the support table, intrasurface temperature distribution on the water becomes uneven, and thermal process to the wafer cannot be achieved uniformly.
The unnecessary films deposited on the surfaces of the support table and the cover peel of comparatively easily at an early stage. Since the cleaning process needs to be carried out before the unnecessary films peel off, maintenance work including the cleaning process needs to be carried out frequently at short intervals. When the support table, namely, a heating structure, is divided into heating zones which can be individually heated and the levels of power supplied to the zones are distributed in a wide range, the support table may possibly break due to the different thermal expansions of the materials forming the zones of the support table.
The present invention has been made in view of those problems to solve those problems effectively.
Accordingly, it is an object of the present invention to provide a support table structure capable of surely suppressing the occurrence of contamination, such as metal contamination, having high heat conductivity, suitable for a high-temperature thermal process and capable of being heated uniformly by wide-range adjustment, and to provide a thermal processing system provided with the support table structure.
Another object of the present invention is to provide a support table structure capable of eliminating the detrimental thermal effect of unnecessary films deposited in patches thereon and of maintaining the surface thereof in a highly uniform intrasurface temperature distribution, and to provide a thermal processing system provided with the support table structure.
A third object of the present invention is to provide a support table structure capable of effectively preventing unnecessary films deposited thereon to reduce the frequency of maintenance work, such as a cleaning process, and to provide a thermal processing system provided with the support table structure.
A fourth object of the present invention is to provide a support table structure including a support table having a plurality of hating zones and capable of maintaining the surface of the wafer in a highly uniform intrasurface temperature distribution by setting differences in driving power flexibility among the heating zones and of performing a special heating process, and to provide a thermal processing system provided with the support table structure.